Low temperature metallizing paint and method of making same



United States Patent 3,352,694 LOW TEMPERATURE METALLIZING PAINT ANDMETHOD OF MAKING $AME Leonard Reed, San Jose, and Donald C. Figone, SanFrancisco, Calif., assignors, by mesne assignments, to VarianAssociates, a corporation of Caiifornia N0 Drawing. Filed June 17, 1963,Ser. No. 288,454 Claims, (Cl. 1061) This invention relates to ametallizing paint composition. More particularly, this invention relatesto a low temperature metallizing paint composition for obtaining avacuum tight metallized surface on ceramic bodies and the method ofobtaining the metallizing paint.

Generally, a ceramic body is metallized by painting the portion of theceramic body to be metallized with a metallizing paint and then heatingthe coated ceramic to sinter a refractory metal, present in the paint,onto the ceramic. The resulting metallized layer generally comprises arefractory metal phase which is extensively penetrated by a non-metallicglassy phase that wets and adheres to both the refractory metal and theceramic body. The metallizing paint may comprise a vehicle whichincludes a binder and a solvent with the refractory metal and the glassyphase material suspended therein. The metallizing paint is applied tothe ceramic body by hand painting, spraying, dipping, silk screening orby any other suitable means. Heretofore in the prior art, the highsintering temperature (1300 to 1600 C.) of many metallizing paints hastended to warp various ceramic bodies. Also, expensive apparatus, suchas high temperature furnaces, etc. are required to produce these highsintering temperatures- Therefore, an object of this invention is toprovide a low temperature metallizing paint.

Another object of this invention is to provide a metallizing painthaving a sintering temperature of about 1000" C.

Still another object of this invention is to provide a metallizing painthaving a sintering temperature of about 1000 C. for producing a vacuumtight metallized layer on ceramic bodies.

A further object of this invention is to provide a method for obtaininga low temperature metallizing paint.

These and other objects of this invention are obtained by a metallizingpaint composition which includes at least one material therein whichacts to reduce the sintering temperature of the refractory metal and themelting temperature of the glassy phase material contained in themetallizing paint. In accordance with this invention, a low temperaturemetallizing paint composition comprises a vehicle including a binder ina solvent. A plurality of metal powders are dispersed in the vehicle andinclude a refractory metal and a quantity of at least one metal whichreduces the sintering temperature of the refractory metal and themelting temperature of glassy phase material. A plurality of glassyphase producing powders are also dispersed in the vehicle. Also, anonmetallic powder, such as boric acid, may be added to the vehicle tofurther aid in reducing the melting temperature of the glassy phasematerial. Further, the powders in the vehicle may be at least partiallycoated with iron to improve the density of the sintered refractory metallayer obtained with the metallizing paint.

This invention, as well as other objects, features and advantagesthereof, will be readily apparent from the following detaileddescription. In accordance with this invention, a low temperaturemetallizing paint is obtained by preparing a vehicle which includes asolvent and a binder. A preferred binder material is nitrocellulose.However, the binder material may be any organic film- Patented Nov. 14,1967 forming substance, such as ethyl cellulose or methacrylate resin,commonly used and well known in the art, which decompose upon heatingleaving little or no residue. A plurality of metal powders are placed inthe vehicle and include a refractory metal selected from the groupconsisting of tungsten, molybdenum and rhenium and a quantity of atleast one metal, selected from the group consisting of copper, nickel,cobalt and iron, for reducing the sintering temperature of therefractory metal and the melting temperature of glassy phase producingmaterial. For purposes of describing and claiming the present invention,metal powders are defined as any one or more of the various powder formsof metal, such as pure metal powder, metal oxide powder, metal hydridepowder, etc. A plurality of non-metallic glassy phase producing powdersare also placed in the vehicle and include by weight a majority ofmanganese dioxide and a minority by weight of silica, and titaniumdioxide. Also, a non-metallic powder, preferably boric acid, may beadded to the vehicle to further aid in reducing the melting temperatureof the glassy phase material. A uniform distribution or suspension ofthe powders in the vehicle is obtained by ball milling the metallizingpaint mix.

According to a preferred example of the present invention, a lowtemperature metallizing paint composition having a sintering temperatureof about 1000 C. is formed by preparing a vehicle which includes abinder and a solvent. One hundred cc. by weight of a preferred solventcomprises about 50 cc. of ethylene glycol monoethyl ether, such asDowenol EE, and 50 cc. of methylethyl ketone. The vehicle is formed byadding by weight about 1.5 grams of nitrocellulose to cc. of thesolvent. A plurality of at least 325 mesh metal oxide powders are addedto the 100 cc. of vehicle and include by weight about 100 to grams of arefractory metal selected from the group consisting of tungsten oxide,molybdenum oxide or rhenium oxide and about 10 grams nickel oxide, about5 grams of copper oxide and about 2 grams of iron oxide. The nickel,copper and iron oxides act to reduce the sintering temperature of therefractory metal, which is preferably tungsten oxide, and also reducethe melting temperature of the glassy phase materials describedhereinbelow. A plurality of at least -325 mesh glassy phase producingpowders are also added to the 100 cc. of vehicle and include about 10.4grams of manganese dioxide, about 4.4 grams of silica, and about 2.2grams of titanium dioxide. Also, about 4.2 grams of boric acid is addedto the vehicle to aid in reducing the melting temperature of the glassyphase material.

A uniform distribution or dispersion of the powders in the vehicle isobtained by ball milling the metallizing paint mix for approximately 48hours. In order to increase the hardness and density of the metallizedlayer produced by the metallizing paint, the ball milling is performedin an iron ball mill with /2 inch diameter iron balls which intimatelycoats at least a portion of the powder particles dispersed in thevehicle with iron from the iron balls by a disintegration commutationprocess.

The metallizing paint may be applied to any suitable ceramic, such as aberyllium oxide ceramic or a high alumina ceramic, that is, onecontaining at least 85% alumina. The sintering temperature of themetallizing paint is about 1000 C. The sintering preferably takes placefor /2 hour in an atmosphere of four parts nitrogen to one part hydrogenhaving a dew point of plus 1000 F. This low sintering temperature is dueto the materials used, such as the copper, nickel and iron. In theabsence of these materials, the sintering temperature of the metallizingpaint would be in the vicinity of 1500 to 1600" C. It is believed thatthe presence of the copper, nickel and iron powders intermingled withthe refractory metal powder causes-this reduction in the sinteringtemperature of the refractory metal. Also, a portion of the copper,nickel and iron exist in ionic form in the glassy phase melt duringsintering and reduce the melting temperature of the glassy phasematerial, that it, the manganese, silica and titanium oxides. The boricacid further aids in reducing the melting temperature of the glassyphase material. The metallizing paint composition described hereinabovein detail is such that at about 1000" C. the glassy phase materialsproduce a manganese-titaniumalumino-borosilicate melt that extensivelypenetrates the refractory metal and wets and adheres to both therefractory metal and the ceramic to form a vacuum tight metallizedsurface on the ceramic body. Tensile strengths up to 12,000 p.s.i. havebeen obtained by utilizing this metallizing paint in conjunction with anoverplate of nickel followed by a copper-silver braze to a copper metalmember.

Although specific quantities of the materials comprising a novel lowtemperature metallizing paint are given hereinabove, it is to beunderstood that these quantities may be varied according to the paintcharacteristics de sired without departing from the spirit and scope ofthe present invention. For example, the metal oxide powders may bereplaced by pure metal powders. Also, the boric acid need not be used inwhich case the metallizing paint will have a sintering temperature ofabout 1000 to 1100 C. Further, the consistency of the paint desired maybe controlled by varying the amounts of the solvent and binder used.Also, cobalt oxide may be used in place of the nickel and/ or copperoxide; and other glassy phase producing materials may be used ratherthan the manganese, silica and titanium described hereinabove.

What is claimed is:

1. A metalizing paint for producing a vacuum-tight metalized surface onceramic, said metalizing paint having a sintering temperature of about1000 C. comprising:

a vehicle including a binder and a solvent;

a plurality of metal powders dispersed in said vehicle, said metalpowders consisting essentially of approximately 85% to 90% by weight ofa refractory metal selected from the group consisting of tungstenmolybdenum and rhenium, and approximately to by weight of at least oneother metal selected from the group consisting of nickel, copper, cobaltand iron; and

a plurality of glassy phase producing powders dispersed in said vehicle.

2. Claim 1 wherein said refractory metal is in oxide form.

3. Claim 1 wherein said other metal is in oxide form.

4. Claim 1 wherein said other metal consists of approximately 60%nickel, approximately 30% copper and approximately 10% iron by weight.

5. Claim 1 wherein said glassy phase producing pow- 4 ders consistessentially of a majority by weight of manganese dioxide and a minorityby weight of silica and titanium dioxide.

6. Claim 1 wherein said glassy phase producing powders consistessentially of approximately of manganese dioxide, 26% silica and 14%titanium dioxide by weight.

7. Claim 1 further including boric acid to reduce the meltingtemperature of the glassy phase producing powders.

8. Claim 7 wherein the proportion of glassy phase producing powders toboric acid is approximately 4:1 by weight.

9. Claim 1 wherein the metal powders and the glassy phase producingpowders are at least partially coated with iron.

10. The method of making a metalizing paint having asinteringtemperature of about 1000 C. comprising the steps of:

preparing a vehicle by combining a binder with a solvent;

placing in the vehicle a plurality of metal powders consistingessentially of a refractory metal selected from the group consisting oftungsten, molybdenum and rhenium and a quantity of at least one metalselected from the group consisting of cobalt, nickel, copper and iron;

placing in the vehicle a plurality of glassy phase producing powders;and

coating the powder particles in the vehicle with iron such as byball-milling the vehicle containing the powders with iron balls.

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2,985,547 5/1961 Luks 117-160 3,093,490- 6/1963 MacKay 1061 3,110,57111/1963 Alexander 117160 X 3,189,504 6/1965 Whittle et a1. 156--2343,227,591 1/1966 Lambert et al 15680 3,290,171 12/1966 Zollman et al.1061 3,293,072 12/1966 Doolittle et al l17138.8

ALEXANDER H. BR'ODMERKEL, Primary Examiner.

J. H. WOO, Assistant Examiner.

1. A METALIZING PAINT FOR PRODUCING A VACUUM-TIGHT METALIZED SURFACE ONCERAMIC, SAID METALLIZING PAINT HAVING A SINTERING TEMPERATURE OF ABOUT1000*C. COMPRISING: A VEHICLE INCLUDING A BINDER AND A SOLVENT; APLURALITY OF METAL POWDERS DISPERSED IN SAID VEHICLE, SAID METAL POWDERSCONSISTING ESSENTIALLY OF APPROXIMATELY 85% TO 90% BY WEIGHT OF AREFRACTORY METAL SELECTED FROM THE GROUP CONSISTING OF TUNGSTENMOLYBDENUM AND RHENIUM, AND APPROXIMATELY 10% TO 15% BY WEIGHT OF ATLEAST ONE OTHER METAL SELECTED FROM THE GROUP CONSISTING OF NICKEL,COPPER, COBALT AND IRON; AND A PLURALITY OF "GLASSY" PHASE PRODUCINGPOWDERS DISPERSED IN SAID VEHICLE.